Auto-steering systems for vehicles are commonly used, e.g. in off-highway machinery such as wheel loaders, excavators, dozers, tractors, harvesters and similar heavy duty machines. Such machines often operate with hydraulic, electro-hydraulic, and electric steering systems. For a system which is operated by a driver, the steering system receives input via a control handle such as a steering wheel or a joystick, and for automatic steering of the vehicle, input may further be received from a GPS system or similar system for automatic positioning and tracking. The input is converted by the steering system into an appropriate hydraulic flow to a hydraulic actuator, e.g. a hydraulic cylinder, which moves a steered element, typically wheels of the vehicle. U.S. Pat. No. 6,052,647 and U.S. Pat. No. 6,539,303 both describe systems for controlling a vehicle along a path by use of GPS technique.
Typically, the input delivered by the positioning and tracking system is a desired path which is described as a radius of a curvature. The steering system is calibrated to translate the received radius into an appropriate hydraulic flow to position the steered wheels correctly relative to the desired curvature. Typically, the systems are calibrated to turn the steered wheels a specific angle for a specific input from the positioning system, and to enable reuse of identical calibration data for several vehicles, each vehicle must be completely identical, and the individual components of the steering system, e.g. the hydraulic actuator, the sensor and the positioning system must be identically configured and positioned relative to other parts of the steering system. Changes in the design of a vehicle and adaptation of new components in the steering system therefore typically require a time consuming recalibration.